1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to circuit breakers including an operating mechanism having a pivoting cradle.
2. Background Information
Circuit breakers of the type having an operating mechanism and a trip mechanism, such as a thermal trip assembly and/or a magnetic trip assembly, which are automatically releasable to effect trip operations and manually resettable following trip operations are common and generally well known in the art. Examples of such circuit breakers are disclosed in U.S. Pat. Nos. 3,849,747; 4,933,653; and 5,008,645.
Such circuit breakers, commonly referred to as “miniature” circuit breakers, have been in use for many years and their design has been refined to provide an effective, reliable circuit breaker, which can be easily and economically manufactured on a large scale. In addition, circuit breakers of this type may be utilized in conjunction with arc fault and/or ground fault trip mechanisms as well.
Circuit breakers of this type include at least one set of separable contacts disposed within a non-conductive housing. Typically, there is a fixed contact attached to the housing and a movable contact coupled to the operating mechanism. The operating mechanism includes a movable operating handle that extends outside of the housing. The operating mechanism further includes an operating arm, upon which the movable contact is disposed, the trip mechanism, and a cradle. The cradle is coupled to a spring and is pivotally disposed between the trip mechanism and the operating arm. One portion of the cradle pivots with respect to the housing while another portion of the cradle has a latch ledge, which is latched by the trip mechanism.
The operating member or handle has essentially two or three stable positions: (1) ON and OFF; or (2) ON, OFF and TRIPPED. In the latter case, the three positions tell the operator what condition the circuit breaker is operating in when viewed. In normal operation, the handle is maintained in the ON position. Then, once the trip mechanism is automatically released, in order to protect electrical circuitry from damage due to an overcurrent condition, such as an overload or relatively high level short circuit, the handle automatically moves to the TRIPPED position. The circuit breaker must then be reset, as is known in the art, by moving the handle beyond the OFF position to a RESET position from which the handle returns to the OFF position when released. The circuit breaker may then be manually operated from the OFF to the ON position, in order to allow the circuit breaker to resume normal operation. In addition, the handle is manually maneuverable from the ON to the OFF position if it is desired to open the protected circuit.
It is known to employ molded material, such as a molded pivot pin, in miniature residential and industrial circuit breakers as a pivot point for the operating mechanism cradle. See, for example, U.S. Pat. Nos. 6,259,339; 6,239,676; 6,040,746; and 5,805,038.
A thermal-magnetic circuit breaker is calibrated, for example, to maintain a current flow of 100% of its rated current and to trip within predetermined times at 135% and 200% of such rated current. However, whenever the circuit breaker housing is made from a stronger, albeit softer, material, the motion of the cradle wears into the molded pivot pin. Hence, the cradle and, thus, its position with respect to the trip mechanism changes, thereby impacting operation of the circuit breaker. For example, thermal calibration of the bimetal trip assembly will change.
U.S. Pat. No. 5,343,179 discloses a miniaturized solenoid operated trip device including a generally L-shaped pivoting trigger member operated by a solenoid to restrain or release a sliding actuator. The L-shaped trigger member has a pivot hole adjacent the junction of two legs of the L-shape, whereby the trigger member is pivotally mounted on a steel pivot pin mounted in a bottom molded housing part via retaining clasps. The sliding actuator is constrained to move back and forth by a slotted structure of the bottom molded housing part.
Current is switched to the solenoid, for example, when an overcurrent condition, undervoltage or ground fault is detected in the load circuit. When current is applied, a solenoid plunger retracts into the solenoid. This rotates the trigger member around the steel pivot pin, releasing an interlock with a mating hook surface on the sliding actuator. An actuator spring propels the sliding actuator outwardly with a dynamic action such that an abutment of the actuator strikes a paddle on a trip bar of a pivoting contact breaking mechanism. The contact breaking mechanism is operatively associated with a contactor cradle or the like to make or break an electrical circuit.
There is room for improvement in circuit breakers including an operating mechanism.
There is also room for improvement in circuit breaker operating mechanisms including a cradle.